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CHICAGO -- More than half of patients who have abdominal computed tomography (CT) scans may be getting extra series of tests that aren't necessary and that lead to increased radiation exposure, researchers said here.

In a retrospective analysis, 52.2% of patients had an unindicated series of scans -- most often delayed-phase imaging, which involves a contrast agent diffusing through blood, tissues, and subsequently organs, said Kristie Guite, MD, of the University of Wisconsin in Madison.

"Our study found that the ALARA principle [As Low As Reasonably Achievable] is not being followed," Guite said at a press briefing at the meeting of the Radiological Society of North America.

Concern about excessive doses of ionizing radiation from medical imaging has been a major concern for patients and the physicians who refer them for scans. The researchers said that much attention has been paid to overall CT use and inappropriate scanning parameters.

However, additional series of scans -- noncontrast or delayed-phase scanning, for example -- are one source of excess radiation that hasn't been looked at.

So they reviewed abdominal and pelvic CT scans for 500 patients that had been forwarded to the University of Wisconsin in Madison for interpretation, which totaled 978 series exams.

They found that about a third of the series exams -- 35.3% of them -- were unindicated. More than half of the patients (52.2%) had had unindicated scans.

The most common additional and unnecessary scans were delayed-phase imaging -- in 77.7% of the 345 unindicated series exams. Delayed-phase scanning allows radiologists to capture images as a contrast agent diffuses through the arteries, into tissues and veins, and ultimately through organs. Delayed-phase imaging is typically indicated after trauma or for renal masses.

"But most patients who get it don't have either of these indications," said co-author J. Louis Hinshaw, MD, of the University of Wisconsin. "They're getting this despite the fact that there's no good indication."

Patients got a mean total radiation dose of 32.9 mSv -- the equivalent of about 1,000 chest X-rays, Guite said. That's 10 times the normal cosmic background radiation humans receive annually, she added.

Guite said about 20% of the records indicated that the patients received more than 50 mSv of radiation, and seven of the 500 patients received greater than 100 mSv in a single scan.

Previous research has shown that doses in excess of 100 mSv may increase risk of radiation-induced cancer, Guite said.

She added that if these unnecessary series scans were eliminated, radiologists could reduce overall radiation exposure by 63% and avoid about 23,000 radiation-induced cancer cases per year in the US.

Hinshaw said he suspects that at many institutions, "there is a lack of focus on selecting CT protocols tailored specifically to answer the clinical question." He also suggested that having the tools and the ability to use them may also set in motion additional tests.

Guite said the most important finding is that "adherence to ALARA does not appear to be widespread at this time."

Robert Zimmerman, MD, of New York-Presbyterian Hospital and Weill Cornell Medical Center, said radiologists need to remember ALARA.

"ALARA is a goal that radiologists have been looking at for several years, and it's not just referring physicians [who are over exposing patients to radiation]. Some of our own radiologists haven't been paying attention to this as they should have," Zimmerman said. "All of us should be much more sensitive."

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